Linear accelerator



2, 1966 .11. an m'r smm 3,263,575

LINEAR ACCELERATOR Filed Aug 5, 1854 INVENTOR. JACK 8. 0772557340 /5 BY fl -fia 5 PM A TTURA/E'KSL United States Patent 3,263,575 LINEAR ACCELERATOR Jack B. Ottestad, La Jolla, Calif., assignor to Impulse Products Corporation, San Diego, Calif., a corporation of California Filed Aug. 3, 1964, Ser. No. 387,079 7 Claims. (Cl. 92-75) This invention relates to linear accelerator devices, and to means for arresting their recoil motion without violence to personnel or surrounding structure which hold the devices.

Linear accelerators of the class which are intended to exert an impact on an adjacent body are well known. One widely known example is the common pneumatic hammer. There is another less Widely known class of these devices, wherein a pair of bodies of unequal mass are forced apart by substantial bursts of energy. The distribution of energy between the bodies is inversely related to their masses, the body of lesser mass moving the greater distance and having the greater energy. The body of lesser mass is ordinarily impacted into an object and there transfers much of its energy to that object. This leaves the other body of greater mass moving in the opposite direction with substantial kinetic energy. This energy must be dissipated before the device can be recycled.

The energy could be transmitted as a shock to the housing much as it is done in common pneumatic hammers. However, this is damaging to persons holding the equipment, and also on the equipment.

It is an object of this invention to provide a linear accelerator with means to enable the residual kinetic energy of the bodies to be dissipated without exerting shock forces on the housing of the device, and without transmitting any shock whatever to a person or structure holding the device.

A linear accelerator according to this invention has a central axis, and includes a first and a second body, each body having a boundary wall. The first body has the greater mass and cross-section normal relative to the axis. The housing has a first and a second bore, both of which open to the atmosphere and which meet at an intersection. The first and second bodies are freely axially shiftlable within the respective first and second bores. They are disposed on opposite sides of the intersection, but this is the only limitation on their position. Means is provided for exerting an axial separative force between the two bodies thereby to move them apart.

An expansible chamber is formed within the first bore between the intersection and the first body which chamber is enlarged by motion of the first body away from the second bore. Fluid entry to this chamber is restricted by a sufficiently close fit of the housing with the boundary wall of the first body and with some portion of the second body, whereby a reduced fluid pressure is generated in the chamber when the bodies are separated. This causes a recoil-resisting force to be exerted against the first body which is a function of the difference between atmospheric pressure and the reduced pressure within the said chamber.

. According to a preferred but optional feature of the invention, handles are placed on the outside of the housing so that the user may press down on then, and if the force exerted by the user exceeds the said force less the weight of the housing, the energy of the first body will be dissipated without any reaction being felt by the user.

The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings in which:

FIGS. 1 and 2 are side elevations partly in cut-away cross-section showing the device of the invention in two operative positions;

FIG. 3 is a top view of FIG. 1; and

FIG. 4 is a fragmentary axial cross-section showing a variation of FIG. 1.

The presently preferred embodiment of a linear accelerator 10 according to the invention is shown in FIGS. 1-3. This device includes a housing 11 having an axis 12 and a pair of handles 13. Although the device is able to operate in any position below the horizontal, it is shown in the vertical position, which is the most common position. The housing includes a first and a second bore 14, 15. The first bore is larger than the second bore. The radii of the bores are identified as r and r They meet at an intersection 16. An annular shoulder 17 extends radially outward from the intersection.

A first and a second body 18, 19 are respectively fitted in the first and second bore. The bores include boundary walls 20, 21 and the bodies include respective boundary walls 22, 23. The contiguous boundary walls are geometrically similar, and are formed as surfaces generated by straight lines maintained parallel to the axis. The most convenient and usual shape is cylindrical.

In the preferred embodiment of the invention as shown, the two bodies make reasonably close fits with the walls of the respective bores. These need not be a full fluid sealing fit, because in some instances it will be desired to permit limited fluid flow at least between the first body and the wall of the first bore, and clearance for this purpose is identified by the letter C in FIG. 3. Whatever the construction, the clearances should be such that the bodies are freely slideable in their respective bores, and so that when they are moved swiftly apart air enters into chamber 24 between the intersection and the first body at such a slow rate as to allow the generation of a reduced pressure therein. This clearance is sometimes called a passage which permits a restricted gas flow.

In this class of device it is customary to exert substantial energy so as to separate the two bodies. Means 25 is provided for this purpose. It includes a source 26 of fluid under pressure such as compressed air which is adapted to be discharged by valve 27 into a compartment 28 which stands above rod 29. The rod is integral with and forms a part of the second body. It will be recognized that introduction of high pressure air into cylinder 28 will force the two bodies apart. A flange 30 is provided which will prevent the second body from separating from the first body. The relative axial dimensions derived from energy and stroke considerations are of no importance to this invention and neither are the specific valving means, nor are means for moving the bodies back together after each separation. Sufilice it to say that in practical devices of this class there are these means.

FIG. 4 illustrates an alternate embodiment of the invention. It shows first and second bodies and first and second bores, but in this case the lower end of the second body has a smaller radius than that of the second bore,

so that there is not a fluid sealing fit at all below the intersection. Instead, rod 29 (which is a part of the second body) makes a sliding sealing fit with a gland 31 formed at the intersection of the two bores so as to permit the entire region within the second bore to stay at atmospheric pressure, while permitting chamber 32 to assume the variable pressures heretofore described in connection with chamber 24. While a fluid seal between gland 31 and the rod constitutes a substantial fluid seal between the second body and the housing, as in FIG. 1, the important difference between these two arrangements is that in FIG. 1 the low pressure is exerted on the upper side of the second body, while this is not the case in the device of FIG. 4.

The initial condition of the device is shown in FIG. 1 with the pressure source charged and the valve closed. At this time the two bodies will be drawn to each other by means which are not shown nor pertinent to this invention, the housing is placed in contact with an object (not shown) which is to be impacted by the second body or by something attached to the second body, and then the valve is quickly opened. Discharge of gas under pressure into compartment 28 drives the two bodies apart with a force equal to the cross-sectional area of the rod times the pressure in the compartment. It may readily be calculated that the distance S traveled by the first body, and the distance S traveled by the second body are inversely related to their masses, the mass of the second body, of course, including that of the rod. Also, the kinetic energies of the bodies are inversely proportional, that is, that the kinetic energy of the second body is greater than that of the first body. The bodies move apart as shown in FIG. 2.

When the second body impacts the object, it transfers its kinetic energy to the object it strikes. The first body does not lose its kinetic energy, because it does not strike anything. It is now necessary to stop this body in order that the cycle may be repeated. It will be noted that as the first body moves upwardly, it is opposed by atmospheric pressure passed through the open top of the first bore. The top will ordinarily be covered and ported. As the firstbody moves up and the second body moves down, a reduced pressure will be generated in chamber 24, which exerts an unbalanced force across the first body tending to slow it down provided it is related to other structures such as the housing. In this case it will be seen that the housing is balanced as to atmospheric pressure for a radial distance equal to the thickness of the outer wall of the first bore, and the radius of the second bore (the radius of intersection 16), and is unbalanced for the distance between the boundary wall of the first cylinder and intersection 16. This annular area bears a diiferential pressure equal to the difference between atmospheric pressure and the reduced pressure inside chamber 24. This differential unbalanced pressure will attempt to move the housing upwardly and must be overcome. The force to overcome it can be derived from the weight of the housing itself, plus downward force exerted on the handles.

This force is surprisingly light and well within the abilities of a user to sustain. For example, in a presently existing device of this class, the area of the circle with radius r is about seven square inches and the area of the circle with radius r is about three square inches, leaving about four square inches of area subject to the difierential pressure. The maximum differential pressure is about 14.7 lbs. per square inch. This represents an unbalanced force which has to be overcome of about 58.8 lbs. The housing itself in this device tends to weigh about lbs., so that in order to overcome this force, the user must lean on the handles with about 50 lbs., which is readily within the capacity of the average man who will use a device of this class. Should he do this, he will then override all upward forces and will, in fact, never feel the force which snubs the first body in its upward motion.

This motion will be resisted by the 58.8 lbs. and will soon exhaust the kinetic energy. At this time the first body will tend to be drawn down by gravity (or return means, if provided) to the position of FIG. 1. Air which may be trapped in chamber 24 can leak out through clearance C between the boundary walls or through porting means, if provided. By means not shown, the pressure source is recharged and the valving placed in condition for recycling.

FIG. 4 illustrates that chamber 32 may differ from chamber 24 in that the second body may be isolated from the reduced pressure region if desired. In this case the annulus representing the area subject to the unbalanced force is bounded by circles with radii r and r It will thereby be seen that this device comprises a linear accelerator which can readily be held or weighted down so as to absorb the recoil forces of the masses without any effect on the user. This is a significant improvement over the common construction of pneumatic hammers and the like, wherein heavy recoil forces have had to be absorbed by the user himself. The force to be exerted is a function of housing mass, annular area, and of pressure differential, all of which are subject to selection in the design of the equipment. The value of the pres sure diflerential can, to a limited degree, be adjusted in use.

This invention is not to be limited by the embodiments shown in the drawings and described in the description which are given by way of example and not of limitation but only in accordance with the scope of the appended claims.

I claim:

1. A linear accelerator having an axis and comprising: a first and a second body each body having a boundary Wall, the first body having the greater mass and the greater normal cross-section relative to the axis; the housing having a first and a second bore, the opposite ends of said bores being exposed to atmosphere, said bores intersecting and being adapted to receive in axially freely sliding relationship the first and second bodies respectively, means for exerting an axial, separative force between the two bodies, thereby to move the bodies apart with energies and for distances inverse to their relative masses, and with the intersection of the bores between them, whereby a region of reduced fluid pressure is formed therebetween, and whereby axial motion of the first mass is resisted by a force equal to the difference in the areas of the bores times the difference of the atmospheric pressure and the reduced fluid pressure between the bodies.

2. A linear accelerator according to claim 1 in which the bodies and bores comprise pistons and cylinders, respectively.

3. A linear accelerator according to claim 1 in which the region of reduced fluid pressure is open to atmosphere through a passage which permits a restricted gas flow.

4. A linear accelerator according to claim 1 in which the first mass makes a substantially fluid-sealing fit with the wall of the first bore.

5. A linear accelerator having an axis and comprising: a first and a second body each body having a boundary wall, the first body having the greater mass and the greater normal cross-section relative to the axis; the housing having a first and a second bore, the opposite ends of said bores being exposed to atmosphere, the said bores intersecting each other; the first mass making an axially freely sliding fit with the first bore, the second mass clearing the wall of the second bore, a rod integral with the second mass and having a lesser cross-section than the second mass; fluid-seal means between the housing and said rod, a chamber thereby being formed between the first mass and the fluid seal means; means for exerting an axial, separative force between the two bodies, thereby to move the bodies apart with energies and for distances inverse to their relative masses, whereby reduced fluid pressure is formed in said chamber as it expands, and whereby axial 5 6 motion of the first mass is resisted by a force proportional References Cited by the Examiner to the difference betv een atmospheric pressure and the UNITED STATES PATENTS reduced fiuld pressure in the chamber.

6. A linear accelerator according to claim 5 in which 2,400,650 5/ 1946 Leave et a1 the chamber is open to atmosphere through a passage 5 3,023,840 4/1962 Leave X which permits a restricted gas flow. 3,200,893 8/1965 Leavell 173 162 X 7. A linear accelerator according to claim 5 in which i the first mass makes a substantially fluid-sealing fit with SAMUEL LEVINE Primary Exammer the wall of the first bore. I. C. COHEN, Assistant Examiner. 

1. A LINEAR ACCELERATOR HAVING AN AXIS AND COMPRISING: A FIRST AND A SECOND BODY EACH BODY HAVING A BOUNDARY WALL, THE FIRST BODY HAVING THE GREATER MASS AND THE GREATER NORMAL CROSS-SECTION RELATIVE TO THE AXIS; THE HOUSING HAVING A FIRST AND A SECOND BORE, THE OPPOSITE ENDS OF SAID BORES BEING EXPOSED TO ATMOSPHERE, SAID BORES INTERSECTING AND BEING ADAPTED TO RECEIVE IN AXIALLY FREELY SLIDING RELATIONSHIP THE FIRST AND SECOND BODIES RESPECTIVELY, MEANS FOR EXERTING AN AXIAL, SEPARATIVE FORCE BETWEEN THE TWO BODIES, THEREBY TO MOVE THE BODIES APART WITH ENERGIES AND FOR DISTANCES INVERSE TO THEIR RELATIVE MASSES, AND WITH THE INTERSECTION OF THE BORES BETWEEN THEM, WHEREBY A REGION OF REDUCED FLUID PRESSURE IS FORMED THEREBETWEEN, AND WHEREBY AXIAL MOTION OF THE FIRST MASS IS RESISTED BY A FORCE EQUAL TO THE DIFFERENCE IN THE AREAS OF THE BORES TIMES THE DIFFERENCE OF THE ATMOSPHERIC PRESSURE AND THE REDUCED FLUID PRESSURE BETWEEN THE BODIES. 